Most of the costs of printing the "variants" (and this applies to the hardcovers, as well) is in printing the bookblock -- and that's identical over both editions. Paying to do a short run of dust jacket or covers, yeah, that's going to be increasingly expensive as the quantities get smaller (not to mention the time spent preparing them), but probably not to the point where it completely erodes the margins -- yet.

(To be honest, I'm surprised they are still doing them at this point, but who knows how long that will last.)

In The Back Of Beyond: My photography blog. Everything seen through the camera of my iPhone.